core/Makefile: pass value of PRODUCT_USE_DYNAMIC_PARTITION_SIZE

Regardless of the value of PRODUCT_USE_DYNAMIC_PARTITION_SIZE
"use_dynamic_partition_size=true" is passed to build_image.sh.
Pass the value of PRODUCT_USE_DYNAMIC_PARTITION_SIZE just like it is
done for other properties.

Test: 1. build a target with fixed partition sizes and
         "PRODUCT_USE_DYNAMIC_PARTITION_SIZE := false".
      2. check the value of "use_dynamic_partition_size" in the
         corresponding system_image_info.txt.
      3. repeat steps 1 and 2 with this fix and see the difference.

Change-Id: Ia121d3d67f554f8ae4e211ad4e2c381a43409f01